A large static magnetic field is used by Magnetic Resonance Imaging (MRI) scanners to align the nuclear spins of atoms as part of the procedure for producing images within the body of a patient. This large static magnetic field is referred to as the B0 field.
During an MRI scan, Radio Frequency (RF) pulses generated by one or more transmitter coils cause a called B1 field. Additionally applied gradient fields and the B1 field cause perturbations to the effective local magnetic field. RF signals are then emitted by the nuclear spins are detected by one or more receiver coils. These RF signals are used to construct the MR images. These coils can also be referred to as antennas. Further, the transmitter and receiver coils can also be integrated into one or more transceiver coils that perform both functions. It is understood that the use of the term transceiver coil also refers to systems where separate transmitter and receiver coils are used.
MRI scanners are able to construct images of either slices or volumes. A slice is a thin volume that is only one voxel thick. A voxel is a small volume element over which the MR signal is averaged, and represents the resolution of the MR image. A voxel may also be referred to as a pixel (picture element) herein if a single slice is considered.
The imaging of bone tissue is in some cases difficult due to the short T2 time present in these highly ordered structures. Typically special pulse sequences are used to image the bone tissue. For example, the journal article Tyler, Damian J., et al. “Magnetic resonance imaging with ultrashort TE (UTE) PULSE sequences: technical considerations.” Journal of Magnetic Resonance Imaging 25.2 (2007): 279-289 discusses several techniques.
Another approach for imaging bone tissue is to perform image segmentation of magnetic resonance images. U.S. Pat. No. 7,920,730 B2 discloses a method for detecting bone and bone disease using MRI images which includes: detecting and segmenting bone borders using dark bone border intensity information from an MRI image; and detecting bone disease within a segmented image region.
Dixon methods of magnetic resonance imaging include a family of techniques for producing separate water and lipid (fat) images. The various Dixon techniques such as, but not limited to, two-point Dixon methods, three-point Dixon methods, and multi-point Dixon methods are collectively referred to herein as Dixon techniques or methods. The terminology to describe the Dixon techniques is well known and has been the subject of many review articles and is present in standard texts on Magnetic Resonance Imaging. For example, the “Handbook of MRI Pulse Sequences” by Bernstein et al., published by Elsevier Academic Press in 2004, contains a review of some Dixon techniques on pages 857 to 887.
The journal article Koch, Kevin M., et al. “Rapid calculations of susceptibility-induced magnetostatic field perturbations for in vivo magnetic resonance.” Physics in medicine and biology 51.24 (2006): 6381 discloses the calculation of an approximated solution to Maxwells's equation to predict macroscopic inhomogeneity of the B0 field induced by susceptibility differences in vivo.